Chaff or 'chop' is chopped up anything, such as plain hay, or lucerne hay, or oat straw. They just put the bale through a machine which chops it into pieces about 1/2 inch long and then it's bagged up and used for horse feeding mostly. It's only as good as the quality of the hay/straw used to make it. In my case it's easier to buy/transport and store than bales of hay. I buy plain meadow hay chaff and lucerne chaff in 20 kilo bags and feed it to the horse, the guinea pigs and now the rabbit too. I also keep a bale of the best hay I can get, for the little guys for the sake of their teeth. They enjoy long crisp hay. But HAY is a problem. I find it very hard to obtain best quality plain meadow hay that's not 50% red clover. We can only buy from local farmers and most of the pasture here is ryegrass/red clover. All hay grown in New Zealand is grown for cattle and sheep and nobody makes specialty hay, special mixtures or anything fancy. If you asked a farmer about timothy or browntop or whatever, he'd just laugh at you!